When a direct current potential is applied across a liquid medium containing charged particles, the particles migrate towards the electrode bearing the opposite charge and deposit thereon. This process is called electrophoretic deposition and is utilized to apply coatings to conductive surfaces for electrical insulation, paint priming, and other purposes.
Electrophoretic deposition from non-aqueous media is accomplished using polymeric emulsions. The composition and formation of these emulsions critically affect the emulsion stability, the particle size of the emulsion droplets, and ultimately, the quality and quantity of the deposited coating. Until now, these polymeric emulsions have been prepared by reacting an organic amine with a polymer in a solution to form an amine salt. The solution was then dispersed in a non-solvent which formed the emulsion. The formation of the salt was believed to be necessary because it was thought that the polymer would not migrate to the electrode unless a charge was placed on it. It was also thought that the reaction of the amine with the polymer to form the salt required heating the amine with the polymer, and that this could not be done efficiently in the presence of the non-solvent. While good emulsions were obtained, results were not totally satisfactory because large polymeric particles precipitated and the size of the particles remaining in the emulsion were generally larger than was desirable for long-term stability and coating uniformity.